The polymerization of olefins using supported catalyst systems is well known. It will also be recognized by those skilled in the art that the use of such supported catalysts is often associated with the development of static charges within the polymerization reactor and subsequent reactor fouling, particularly in gas phase or slurry polymerization reactors. Severe reactor fouling may cause such problems as poor heat transfer; the formation of polymer agglomerates or sheets which adhere to the reactor walls; plugging of the polymer discharge system; and in severe cases, the development of large “chunks” which can force a reactor shut down.
Efforts to mitigate reactor fouling problems are widely reported in the patent literature.
The use of a salt of a carboxylic acids, especially aluminum stearate, as an antifouling additive to olefin polymerization catalyst compositions is disclosed in U.S. Pat. No. 6,271,325 (McConville et al.; to Univation); and U.S. Pat. No. 6,281,306 (Oskam et al.; to Univation).
The preparation of supported catalysts using an amine antistatic agent, such as the fatty amine sold under the trademark KEMANINE AS-990, is disclosed in U.S. Pat. No. 6,140,432 (Agapiou et al.; to Exxon) and U.S. Pat. No. 6,117,955 (Agapiou et al.; to Exxon).
Antistatic agents are commonly added to aviation fuels to prevent the buildup of static changes when the fuels are pumped at high flow rates. The use of these antistatic agents in olefin polymerizations is also known.
For example, an aviation fuel antistatic agent sold under the trademark STADIS™ composition (which contains a “polysulfone” copolymer, a polymeric polyamine and an oil soluble sulfonic acid) was originally disclosed for use as an antistatic agent in olefin polymerizations in U.S. Pat. No. 4,182,810 (Wilcox, to Phillips Petroleum). The examples of the Wilcox '810 patent illustrate the addition of the “polysulfone” antistatic agent to the isobutane diluent in a commercial slurry polymerization process. This is somewhat different from the teachings of the earlier referenced patents—in the sense that the carboxylic acid salts or amine antistats of the other patents were added to the catalyst, instead of being added to a process stream.
The use of “polysulfone” antistatic composition in olefin polymerizations is also subsequently disclosed in:
1) chromium catalyzed gas phase olefin polymerizations, in U.S. Pat. No. 6,639,028 (Heslop et al.; assigned to BP Chemicals Ltd.);
2) Ziegler Natta catalyzed gas phase olefin polymerizations, in U.S. Pat. No. 6,646,074 (Herzog et al.; assigned to BP Chemicals Ltd.); and
3) metallocene catalyzed olefin polymerizations, in U.S. Pat. No. 6,562,924 (Benazouzz et al.; assigned to BP Chemicals Ltd.).
The Benazouzz et al. patent does teach the addition of STADIS™ antistat agent to the polymerization catalyst in small amounts (about 150 ppm by weight).
However, in each of the Heslop et al. '028, Herzog et al. '074 and Benazouzz et al. '924 patents listed above, it is expressly taught that it is preferred to add the STADIS™ antistat directly to the polymerization zone (i.e. as opposed to being an admixture with the catalyst).
We have discovered that supported olefin polymerization catalysts prepared with large amounts of a polysulfone-containing antistat provide surprisingly good polymerization activity and excellent antistatic performance.